This application claims the benefit of Korean Application No. 2002-44453, filed Jul. 27, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetron for microwave ovens, and more particularly, to strip rings of a magnetron having predetermined geometrical configurations to increase the efficiency of the magnetron.
2. Description of the Related Art
Generally, a magnetron includes an anode, and a cathode which discharges thermions. The thermions are spirally moved by an electromagnetic force to reach the anode. At this time, a spinning electron pole is generated around the cathode by the thermions and an induced current is generated in an oscillation circuit of the anode, so as to continuously stimulate an oscillation. The oscillation frequency of the magnetron is generally determined by the oscillation circuit, and has high efficiency and high output power.
The above-described magnetron is widely used as parts of home appliances, including a microwave oven, as well as parts of industrial applications, such as a high-frequency heating apparatus, a particle accelerator and a radar system.
FIGS. 1 to 3 show the construction of a conventional magnetron.
As shown in FIG. 1, the magnetron includes a positive polar cylinder 101 made of, for example, an oxygen free copper pipe, and a plurality of vanes 102 which are disposed in the positive polar cylinder 101 and constitute a positive polar section along with the positive polar cylinder 101. The vanes 102 are radially arranged at regular intervals to form a cavity resonator. An antenna 103 is connected to one of the vanes 102 to induce harmonics to the outside.
Referring to FIG. 2, a large-diameter strip ring 104 and a small-diameter strip ring 105 are disposed on upper and lower portions of the vanes 102, respectively, to alternately and electrically connect the vanes 102 so that the vanes 102 alternately have the same electric potential. Rectangular vane channels 202 are formed in the vanes 102, respectively, to allow the strip rings 104 and 105 to alternately and electrically connect the vanes 102, and cause each opposite pair of vanes 102 to be disposed in an upside-down manner.
According to the above-described construction, each opposite pair of vanes 102 and the positive polar cylinder 101 constitute a certain inductive-capacitive (LC) resonant circuit.
Additionally, a filament 106 in a form of a coil spring is disposed in an axial center portion of the positive polar cylinder 101, and an activating space 107 is provided between radial inside ends of the vanes 102 and the filament 106. A top shield 108 and a bottom shield 109 are attached to a top and bottom of the filament 106, respectively. A center lead 110 is fixedly welded to a bottom of the top shield 108 while passing through a through hole of the bottom shield 109 and the filament 106. A side lead 111 is welded to a bottom of the bottom shield 109. The center lead 110 and the side lead 111 are connected to terminals of an external power source (not shown), so as to form a closed circuit in the magnetron.
An upper permanent magnet 112 and a lower permanent magnet 113 are provided to apply a magnetic field to the activating space 107 with the opposite magnetic poles of the upper and lower permanent magnets 112 and 113 facing each other. An upper pole piece 117 and a lower pole piece 118 are provided to induce rotating magnetic flux generated by the permanent magnets 112 and 113 into the activating space 107.
The above-described elements are enclosed in an upper yoke 114 and a lower yoke 115. A reference numeral 116 designates cooling fins which connect the positive polar cylinder 101 to the lower yoke 115 and radiate heat generated in the positive polar cylinder 101 to the outside through the lower yoke 115.
Referring to FIG. 3, with reference to FIG. 1, as power is applied to the filament 106 from an external power source (not shown), the filament 106 is heated by an operational current supplied to the filament 106, and thermions are emitted from the filament 106. A thermion group 301 is produced in the activating space 107 by the emitted thermions. The thermion group 301 alternately imparts a potential difference to each neighboring pair of vanes 102 while being in contact with front ends of the vanes 102, being rotated by the influence of a magnetic field formed in the activating space 107 and being moved from one state xe2x80x9cixe2x80x9d to the other state xe2x80x9cf.xe2x80x9d Accordingly, harmonics corresponding to a rotation speed of the thermion group 301 are generated by the oscillation of the LC resonant circuit formed by the vanes 102 and the positive polar cylinder 101, and are transmitted to the outside through the antenna 103.
Generally, a frequency is calculated by the equation:   f  =      1          2      ⁢              xe2x80x83            ⁢      π      ⁢              LC            
where L is an inductance and C is a capacitance. The values of the variables of the equation are determined by the geometrical configurations of circuit elements. Accordingly, the configurations of the vanes 102 constituting a part of the LC resonant circuit are principal factors that determine the frequency of the harmonics.
An oscillation frequency of a magnetron for microwave ovens is fixed to a frequency of 2,450 MHz. Since the magnetron for the microwave ovens has a fixed frequency, the magnetron has to be precisely adjusted to the frequency of 2,450 MHz during a production thereof. Although the magnetron has a fixed frequency, the oscillation frequency of the magnetron varies in a range from about xc2x110 to about xc2x115 MHz around a central frequency by the variation of a load under actual operational conditions.
Although, in practice, the magnetron generates a variety of frequencies, a single prominent frequency is specified by a frequency measuring process, and referred to as the oscillation frequency of the magnetron. To set the oscillation frequency of the magnetron in the positive polar cylinder 101, the large-diameter strip ring 104 and the small-diameter strip ring 105, as well as the vanes 102, play principal roles. That is, electric phases of the large-diameter and small-diameter strip rings 104 and 105, which alternately connect the alternately arranged vanes 102 to allow each set of vanes 102 to have the same potential, are changed as electric phases of the vanes 102 are changed. The large- and small-diameter strip rings 104 and 105 oscillate while experiencing the alternate change of the electric phases. A certain amount of electrostatic capacity exists between the large-diameter and small-diameter strip rings 104 and 105 facing each other, and a certain electric oscillation is generated therebetween, generating an unwanted frequency called a parasitic frequency.
Accordingly, a minute frequency is set using the large- and small-diameter strip rings 104 and 105. The shapes and sizes of the large- and small-diameter strip rings 104 and 105, which are fixedly mounted in the magnetron, determine an electrostatic capacity between the large-diameter and small-diameter strip rings 104 and 105, and a frequency related to the electrostatic capacity is generated. Hence, the magnetron is designed to adjust its frequency by controlling the shapes and sizes of the large-diameter and small-diameter strip rings 104 and 105, and is required to have an entirely symmetrical configuration. Generally, the change of the frequency of the magnetron changes a Q value that determines the efficiency of the magnetron, and accordingly, changes the efficiency of the magnetron.
In the conventional magnetron, the large-diameter strip ring 104 has a geographical configuration of an inside diameter of 17.2 mm, an outside diameter of 18.6 mm, a thickness of 0.7 mm and a height of 1.5 mm, while the small-diameter strip ring 105 has a geographical configuration of an inside diameter of 13.9 mm, an outside diameter of 15.35 mm, a thickness of 0.725 mm and a height of 1.5 mm. A Q value that determines the efficiency of the magnetron having such geographical configurations is about 1,850. In the past, many attempts have been made to increase the Q value without success while maintaining the oscillation frequency of the magnetron at 2450 MHz.
Accordingly, an aspect of the present invention is to provide a magnetron for use in, for example, microwave ovens, which incorporates therein a large-diameter strip ring and a small-diameter strip ring having improved geometrical configurations. The large-diameter and small-diameter strip rings of the present invention change a frequency generated in the magnetron and increase a Q value so as to improve the quality of the frequency and the efficiency of the magnetron.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and/or other aspects of the present invention, there is provided a magnetron for microwave ovens, comprising a positive polar cylinder, a plurality of vanes which constitute a positive polar section, along with the positive polar cylinder, and a large-diameter strip ring and a small-diameter strip ring which are disposed on an upper portion and a lower portion of the vanes, respectively, and alternatively and electrically connect the vanes to one another. The large-diameter strip ring has inside and outside diameters which are in a range of 17.1 mm to 18.01 mm and 18.6 mm to 19.6 mm, respectively. The small-diameter strip ring has inside and outside diameters which are in a range of 13.4 mm to 14.4 mm and 14.9 mm to 15.9 mm, respectively. The large-diameter and small-diameter strip rings have a height which is in a range of 1.55 mm to 1.65 mm. According to an aspect of the present invention, the distance between the large-diameter and small-diameter strip rings is maintained in an error range of 2.20 mm.